Abstract

A new, to our knowledge, method for measuring the wavelength
dependence of the transit time, material dispersion, and attenuation of
an optical fiber is described. We inject light from a 4-ns
rise-time pulsed broadband flash lamp into fibers of various lengths
and record the transmitted signals with a time-resolved
spectrograph. Segments of data spanning a range of approximately
3000 Å are recorded from a single flash-lamp pulse. Comparison of
data acquired with short and long fibers enables the determination of
the transit time and the material dispersion as functions of wavelength
dependence for the entire recorded spectrum simultaneously. The
wavelength-dependent attenuation is also determined from the signal
intensities. The method is demonstrated with experiments using a
step-index 200-µm-diameter SiO2 fiber. The
results agree with the transit time determined from the bulk glass
refractive index to within ±0.035% for the visible
(4000–7200-Å) spectrum and 0.12% for the UV (2650–4000-Å)
spectrum and with the attenuation specified by the fiber manufacturer
to within ±10%.

Figures (6)

Transit time per unit length. The green asterisk
represents the absolute measurements performed at 4000, 6700, and 8500
Å. The red, yellow, blue, and magenta curves are measurements
performed with the time-resolved spectrograph. The black curve was
derived from the bulk glass refractive index.

(a) Lineout averaging over 45-Å interval centered at
5156 Å, from the 181.08-m-long fiber data shown in Fig. 3. The
smooth curve is a fast Fourier transform of the data. (b)
Relative transit time for two different fiber lengths. The actual
distance between the two lines is irrelevant.

Material dispersion obtained by differentiation of the
curves displayed in Fig. 1. Red is the dispersion of the visible
data. Magenta, orange, and blue are the UV data sets, and black is
the dispersion of the manufacture’s data.